Problems setting up Low Z injectors.

[DaveT]

Hi Guys,

I may be being really dumb here or I may well have missed something but I'm having a few issues setting up my Siemens 55LB Low Impedience injectors. MS2 V3 Running fuel only at the moment.
The manual states :

PWM Time Threshold = 1.0 millisecond, and
PWM Current Limit (%) = 75% (30% if you have the flyback board installed). ** Flyback installed so 30% **

When I acually try and set them up moving the values down "until the idle quality deteriorates" it really doesn't make much difference.
At one stage I had :
Injector open time(ms) = 0.9
PWM Current Limit(%) = 1
PWM Time Threshold(ms) = 0.9
It idled badly but it still idled, I've now moved them up a little to:
Injector open time(ms) = 1.1
PWM Current Limit(%) = 13
PWM Time Threshold(ms) = 1.1
I'm really unsure of if its actually right or not?

Any help, pointers & tips greatly apreciated. Or if anyone in the UK North london area willing to have a brief chat / look...

Dave

[Bernard Fife]

Dave,

Your engine is likely idling on the time threshold.

Try changing the open time and time threshold to 0.7, I suspect that will make a big difference to the "until the idle quality deteriorates" behavior.

Lance.

[DaveT]

Thanks for your reply,

Went out this evening fired her up and moved the 2 values down to 0.7. 0.8 It started running badly and 0.7 it died. moved the values back up to 1.0 and it started again just fine. moved the 'PWM Current Limit %' up and down but that didnt make any difference...

Dave

[Bernard Fife]

Dave,

You need to increase the PWM% to about 30% first. Then decrease the time threshold/opening time to about 0.7 or 0.8, and play around with the PWM% after you have done that.

Lance.

[DaveT]

Thanks for your reply,

Oops, I think i missunderstood you there. OK just been out again,
1) started her up & increased PWM% to 30%
2) lowered time threshold and opening time, at 0.9 it started running rough and 0.8 running really rough.
3) Slowly started decreasing PWM%
4) at 17% / 18% made a noticable difference.
5) As per manual instructions increased time threshold and opening time by 0.3ms. Now set at 1.2ms
6) as per manual instructions increased PWM% by 3 to 5%. Now set at 20%

Injector open time(ms) = 1.2
PWM Current Limit(%) = 20
PWM Time Threshold(ms) = 1.2

Does this sound about right...?

Many thanks

Dave

[Bernard Fife]

Dave,

Yes, that sounds right.

The other thing you have to check is that the engine still runs well at longer pulse widths. Winging the throttle will bring the accel enrichments into play, and increase the pulse widths a lot, so that's how I do a check of the PWM% initially (if it is too low, the engine will cough and stumble when it tries to rev - assuming the accel enrichments are anywhere near close - if it does stumble, first try doubling the accel enrichments , and if that doesn't help, then increase the PWM% by 3% or so).

If that works fine, then I try WOT while driving and at lower rpms to make sure there are no problems with the injectors shutting down early because the PWM% is too low. Then try WOT to the redline, and if all is good (it should be) you are ready to start tuning everything else!

Lance.

[DaveT]

Lance,

Thanks for your reply, had an hours play with the card again last night. I spent a few mins bliping the throttle and it reved up fine. I then decided to take it up and down the road a bit. I had to get a bit of the VE table dialed in a bit. Problem I had is that mainly whilst accelerating it would just start surging and caughing, looking at the logs it was going really lean then really rich and back again. I gently tweaked the PWM Current Limit(%) down and it got better and better. At them moment PWM Current Limit(%) = 14%

Does it sould right what I've done??

Many thanks

Dave

[Bernard Fife]

Dave,

Yes, that sounds about right. Now you have to tune the VE table and accel enrichments (as described in the manual).

Lance.

[DaveT]

Lance,

Perfect, thankyou very much!
Yeah I'll denote some serious time, reading and investigation to the VE table...
I think I have the accel inrichment about right but it doesm't seem to come in quite quick enough. I always get a lean - rich AFR wobble when dabbing the throttle, normal or can I make it some how detect / react a bit quicker?

Many thanks

Dave

[floppy]

What is your idle pulse-width? I always had a tough time tuning the injectors when my PW was in the 1.2-1.6 range. I followed the directions but never seemed to recognize a significant change. After lowering my req fuel and adjusting the ve up accordingly and going from 4 squirts to 2 I now have idle pw"s around 2.2 and the injector tuning is more reactive. This is on two different engines; a sbc with tbi and a 500 cad with 4 port injectors in the TB,all low-z.